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P. J SPRAGUE.

ELECTRIC MOTOR AND GENERATOR.

No; 315,182. Patented Apr. 7, 1885.

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UNITED STATES PATENT @rricE,

FRANK J. SPRAGUE, OF NEYV YORK, N. Y.

ELECTRIC MOTOR AND GENERATOR.

SPECIFICATION forming part of Letters Patent No. 315,182, dated April 7, 1885.

Application filed July 19, 1884.

To all whom it may concern:

Be it known that I, FRANK J. SPRAGUE, of

New York, in the county and State of New entially-wound electro-dynamic motors and dynamo-electric generatorsin which the main field-coil is shunted around the armature alone, the series or governing coil being outside the terminals of the main field-shunt. My object is to render such motors and generators selfregulating, so that the motor will run at a constant speed under varying loads on either a constant potential or a constant current circuit, or the generator may develop a constant current or a constant electro-motive force.

The invention was designed with especial reference to motors, and I shall therefore describe it more particularly in that connection, explaining, however, its adaptability to dynamo-electric machines used as generators.

I have found that a certain proportion must exist between the series-coil and the shuntcoil in machines of this character, whether used with constant potential or constant current, in order that they may be perfectly selfregulating, and it is in this way of proportioning the coils that my invention mainly consists.

For the class of machines mentioned the proportions which I have devised are the same in all cases, and whether the machine is used with constant current or constant potential,al-

. though the numerical values will depend upon the current and potentials used and the power required. It follows, of course, that a motor wound according to my invention may be used either on a constant current or a constant potential circuit,and will run ata constant speed in either case.

My invention can be most readily set forth and the above statements shown to be correct by a mathematical demonstration.

The magnetic moment of a coil may be defined as the product of the amperes flowing therein by the number of turns, and if the main and governing coils are practically similarly situated with regard to the field-magnet (No model.)

cores the magnetic field may be considered as proportional to the effective magnetic momentthat is, to the difference of the magnetic moments of the shuntand series fields, so long as we are working on a straight or nearly straight line characteristic. This characteristic can be determined for any particular cores in any of the well-known ways-for instance, by running the motor as a dynamo at a constant speed, passing variable known currents through the field-coils and noting the potential existing at the free armature-terminals.

For a properly-constructed motor the fieldmagnet must at no time be too highly saturatedthat is, it must be worked with a characteristic which is a straight or very nearly a straight line. As will be pointed out later, some deviation maybe allowed, but not much.

I will first consider the motor with varying loads in a constant potential circuit and running at constant speed.

Let f denote the resistance of the main or shunt field-coils; m, the number of turns therein; r, the resistance of the differential or series field-coils, and a the number of turns; R, the resistance of the armature; E, the initial potential at the terminals of the motor; 6, the counter electro-motive force set up in the armature; O, the total current flowing over 0*. Then the potential existing at the shunt-terwhence G=; f work done :0

But since 0 can be expressed in terms of e and constants, the work can be also ErG expressed in terms of c and constants m shunt-current, nO seriescurreut, m

nO==efi'ective moment.

E j(Ee)+ER for all potentials so long as we work with a 7 T l-(fdf(Ee)+ER straight-line characteristic; but it must be f with 'a theoretical efficiency of not less than 70 fifty per cent, for if we go below this the gov- 5 But our condltlons are Such that erning-coil works in the wrong direction.

Er%-I%T5 f( +ER Referring to the equation it will 8 m f fR+(j-+R) be seen thatm and f+R can be increased in he 75 Z same ratio. This means that the determined Er f W f(E 6,)+ER constant speed of the motor can be varied for any given potentialalso m andn can be inf creased in the same ratidthat is, if means lf +(.fd "[ff are provided for varying the effective mag- 80 e 6/ [f +(f-l- [f( netic moments of shunt and series coils, the f [f l motor can be set to run at different determined f [f( speeds.

I will now consider the motor with constant mEefR mEe f r mErR-mer fE+mer f cspeed, varying load, and constant current. 5

merERenf E+enf e-e7y"ER: Let the turns, resistance, &c., be designated mEc f R+mEd f r-l-m Ee'rRmer f E-l-mevf 0 as before. E is the variable potential at the -merERcnf*E+ enf eenfER terminals of the shunt-field, and e the corre- Ganceling, we have mfB(ee):nf (e' e)-lsponding counter electro-motive force. \Ve

m f+R must eliminate E and express the work in 9 nRf e 6) R That the terms of e and constants. 0 depends on speed 5 her of turns in the shunt main field-coils'bear and Strength of field; but Since Speed 1S the same ratio to the number of turns in the E series differential field-coils as the sum of the smut 6 depends 011 the eld alone. 7- our resistances of the shunt field-coils and the ar: 99 mature bear to the resistance of the armature. Tent shunt'fiem; current 51mm 3 This is the law of windin for a machine of H this character, and so wou d the machine will 551 1 ent m Sellesifiem 4 the} efole be perfectly self-regulating for any constant K ;wheneefRKzElH-(E-e)f, or

t L IOO glrioingal and for any load up to the maximum 2 Z 2 2 +9 Our conditions are 3 A peculiarity of machines so wound, which f f+ I will now describe, is pointed out in connection with the other class of compound wound g f+R motors in the application already referred to. e mRK-Hnc' I05 The ratio of the magnetic moments of the W" 4 shunt and series fields ins- ER 1 I mEmr e mRK +mcfaK ltnK or emRK+meejhKcRnKc:c'mRK+mac rro -fnKcRnKe 01f(E-c +nER or (6--6')Z)LRI 66 )f MI (ee) RnK,

I -Hf't or l:- This is the same law of wind D R a 72/ or m {U jZE l Z E 6)+ER] ing that holds when a machine of the same I15 Hezo this becolgles class is used for constant potential, and the P same remarks in regard to the zero-field apply I as in the former case; also, as in the former f m case, the speed for any given current can be i, b t flZ:-fi Hence th ti Varied by varying the resistance and turns or 120 "UHD n R the effective turns. becomes L is to Say if a motor of It follows from the foregoing that a machine m1 depending for its regulation upon this differthis character is at rest and the series-coil in ential winding will regulate with a constant its normal governing position, if circuit be current only when working at less than fifty 5 closed to the motor, a zero-field, or nearly so, per cent. armature efficiency, and that the will be produced; for under these circumsame machine with the same winding will stances the magnetic moments are equal, and regulate on a constant potential circuit only either the motor will not start at all, or if it when working at over fifty per cent. armature does start will run at a very great speed, take efficiency. 3 the maximum current at any given potential, The law above set forth is for pure electroand do little work, or none at all. I would dynamic motors. If there is any permanent again state what I have already pointed out, magnetism, as in hard cast-iron, or where perthat the motor will regulate itself perfectly manent steel magnets are used,the law ofwinding is modified in so far as the residual or permanent magnetism is the equivalent of an elec tro-magnetic moment; butin this case,too,there should exist a zero-field if the governing'coil is normally closed when the motor is at rest. I may here point out the fact that even with a slight flattening of the field characteristic the motor wound according to my invention may be self-regulating, because of the distortion of the lines of force by the current in the armature.

A motor constructed with different propon tions than those herein set forth, or with a much curved field characteristic,may regulate to a certain extent, but not with the same range that I obtain. WVith a high potential the speed of such a motor will at first drop as the load is increased, then come to normal, then increase, and if the load be still further augmented then stop and reverse, because the governing-coil becomes predominant, or it will drop and then increase to normal with the maximum load, but if put on any higher potential will act as in the instance first cited.

The fact, hereinbefore pointed out, that in the best self-regulating motor there is a zero or very weak field when the motor is started, necessitates, especially when it is desired to start at a speed not greater than the normal, or when there is any load on the motor, in which case there is danger of burning out, the use of devices whereby the action of the governing-coil may be modified. This may be done by the introduction of a resistance, by shunting the coil with a resistance, or by the variable shunting of the armature upon the main fieldcoils. I prefer, however, to use a switch to short-circuit the governing-coil,or to short-circuit and reverse it. It itis reversed, then the first rush of current makes a very strong field, instead of reducing it to zero, or nearly so, increases the rotary effort, and prevents the burning out of the machine. As an instance, if a constant potential motor have the series-coil reversed when the circuit is closed, if there is margin enough on the field characteristic, we will have a field twice as strong as the strongest normal field, four times the strength when the motor is doing its maximum work per unit of time, and a momentary rotary effort eight times that existing when the maximum work is on. As soon as the speed comes up the governing-coil is shortcircuited and then reversed, and then the motor is self-regulating.

In a machine wound according to my invention if the maximum work per turn is exceeded when the governing-coil is normal, the motor will slow down and stop with a zero field hence it is sometimes desirable to provide, in connection with the reversing-switch for the series-coil, automatic devices for operating the same controlled by variations in current, so that if at any time the maximum work per turn is accidentally exceeded the governing-coil will be short-circuited and re versed, and thus the rotary power and counter electromotive force will be increased and the motor prevented from stopping or burning out.

The proportions above described are equally applicable to the winding of the field-magnets of dynamo-electric generators, the action being simply reversed in these machines.

lIy invention is illustrated in the annexed drawings, in which Figure l is aview, partly in diagram, of a motor embodying my invention; Fig. 2, a diagram illustrating an automatic arrangement for the seriescoil switch for a constant potential circuit. Figs. 3 and are diagrams illustrating the variable shunting of the armature upon the main field, and Fig. 5 is a diagram of an automatic arrange ment of the series-coil switch adapted for a constant-current circuit.

Like letters refer to corresponding parts in all these figures.

The motor shown in Fig. 1 is one having field-magnet cores extending in different directions from the same pole-pieces. My in vention is, however, applicable to any other usual arrangement of field-magnets.

A is the armature, and B O D Eare the field-magnet cores. The coarse differential coil a is in series with the armature, and the finer main coil 1) in a shunt around the armature alone. These coils are to be wound according to the proportions hereinbefore specified. It is of course understood, however, that such proportions are not in reality illustrated in the drawings, which are intended only to show the general arrangement of the circuits.

F is the reversing-switch for the series-coil. It may have any one of three positions. In that shown in Figs. 3 and +t the coilis directly in circuit and opposes the shunt-coil b. As in Figs. 1 and 2, current is reversed in the coil, and it therefore assists the shunt-coil.

In its intermediate position, which is not il' lustrated in the drawings, the movable contacts cross the stationary ones and short-circuit or cut out the coil. \Vhen the motor is started the coil is reversed, as has been already explained, and as soon as the proper speed is reached it is short-circuited and thrown back to its normal position again.

The automatic device for the switch shown in Fig. 2 is a solenoid, G, placed in the armature-circuit, and havingits movable spring retracted core 0 connected with switch F. If the maximum load or work per turn on the motor is exceeded, so that too much current passes in the armature and series coil, such excessive current causes the solenoid to move the switch and first short-circuit and then reverse the series-coil. The switch is also provided with the handle 0, for working it by hand in starting the machine. At a normal current that is, with any load up to the maximumthe spring keeps the switch in its normal position with the current direct in the seriescoil.

In the arrangement shown in Fig. 5 the solenoid G is placed in the shunt field-circuit, this being for a constant-current circuit. An increase of load and armature-current diminishes the current in the shunt and weakens the solenoid, so that the spring moves the core to reverse the current in the series-coil.

Figs. 3 and 4. illustrate the gradual throwing into circuit of the armature. The terminals 1) p are movable upon the sections of the main field-coils, a suitable commutator being employed. Fig. 4 shows the closed field-circuit set forth in my application No. 134,321.

I do not claim herein, broadly, the motor wound so as to produce a zero-field if circuit is closed when the motor is at rest, this being claimed in my application Serial No. 188,146.

What I claim is 1. A compound wound electrodynamic motor or dynamo-electric generator having its two field-coils proportioned substantially as hereinbefore set l'orththat is,so that the number of turns in the shunt-coil bears the same ratio to the number in the seriescoil as the sum of the resistances of the shunt-coil and the armature bears to the resistance of the armature.

2. An electro-dynamic motor having two sets of field-magnet coils whose magnetizing effects are equal, or nearly so, and opposed, if circuit is closed, to both sets of coils when the motor is at rest, one of said sets being in series with the armature and the other in a shunt around the armature alone.

3. An electro-dynamic motor having two sets of field-magnet coils whose magnetizing effects are equal, or nearly so, and opposed, if circuit is closed,to both sets of coils when the motor is at rest, one of said sets being in series with the armature and the other in a shunt around the armature alone, in combination with means for modifying the magnetizing effeet of said series-coils, substantially as set forth.

4. An electro-dynamic motor having two sets of field-magnet coils whose magnetizing effects are equal, or nearly so, and opposed, if circuit is closed, to both sets of coils when the motor is at rest, one of said sets being in series with the armature and the other in a shunt around the armature alone, in combination with means for short-circuiting the said series coils, substantially as set forth.

5. An electro-dynamic motor having two sets of field-magnet coils whose magnetizing effects are equal, or nearly so, and opposed, if circuit is closed, to both setsof coils when the motor is at rest, one of said sets being in series with the armature and the other in a shunt around the armature alone, in combination with means for reversing the current in said series-coils, substantially as set forth.

6. An electro-dynamic motor having two sets of field-magnet coils whose magnetizing effects are equal, or nearly so, and opposed, if circuit is closed, to both sets of coils when the motor is at rest, one of said sets being in series with the armature and the other in a shunt around the armature alone, in combination with an electro-magnetic device in the shunt field-circuit for modifying the magnetizing effect of the said series-coils, substantially as set forth.

7. An electro-dynainic motor having two sets of fieldmagnet coils whose magnetizing effects are equal, or nearly so, and opposed, if circuit is closed, to both sets of coils when the motor is at rest, one of said sets being in series with the armature and the other in a shunt around the armature alone, in combination with a short-circuiting and reversing switch for said series-coils, and an electromagnetic device in the shunt field-circuit for moving said switch, substantially as set forth.

This specification signed and witnessed this 2d day of July, 1881-.

FRANK J. SPRAGUE.

"Witnesses:

B10111). N. DYER, ALFRED W; KIDDLE.

It is hereby certified that in Letters Patent No. 315,182, granted April 7, 1885, upon the application of Frank J. Sprague, of New York, New York, for an improvement in Electric Motors and Generators, certain errors appear in the printed specification requiring correction, as follows: (1.) Line 81, page 1, to line 8, page 2, inclusive, should read as follows: Then the potential existing at the shunt-terminals will be E1-O;

:shunt current; =armature current; =O, or ERTOR+fE-7fG-Qf=ORf, or (JR/"+17%+1RO=fE- "+ER, whence U: Work (10116"6 But since 0 can be ex 3 s l 'n t s f l f B re sec 1 elm o fire-ail; constants, the work can be also expressed in terms of c and constants. m :shunt moment; nG=series moment; m f -n(]=efiective moment ,,f( J' +(f+ f e+ |vfE+(f+B) r' (2.) In line 18, page 2, for mE'rR read mEcrR.

(3.) In line 109, page 2, the sign should be inserted after 5 (4.) In the 2d, 3d, 4th, 5th, 6th, and 7th claims, in the 4th line of each of said claims, the comma after the word closed should be omitted;

And it is certified that the proper corrections have been made in the files and records pertaining to the case in the Patent Oflice, and should be read in said Letters Patent to make the same conform thereto.

Signed, countersigued, and sealed this 19th day of May, A. D. 1885.

[SEAL] H. L. MULDROXV,

Acting Secretary of the Interior. Gouutersigned:

M. V. MoNTeoMnRY,

Conwn iss ioner of Patents.

It is hereby certified that in Letters Patent No. 315,182, granted April 7 1885, upon the application of Frank J. Sprague, of New York, New York, for an improvement in Electric Motors and Generators, certain errors appear in the printed specification I'BQlllTlllgCOII'BOiZlOfl, as follows: (1.) Line 81, page 1, to line 3, page 2, inclusive, should read as follows: Then the potential existing at the shunt-terminals will be E-TG;

]] ==shunt current; =armature current; B =G, or ER-1"GR+fE-rfO-e =OBf, or GRf+afO+rRG=fE-ef+ER, whence C: f(Ee)+ER k d E1"O'e B t O b 1 v f f +19), Wor one e* u since can e expressec 1n teims 0 E0 ang constants, the Work can be also expressed in terms of e and constants. m 7. =shuntmoment; n0=series moment; m -n(3=effectivc moment f "r en e (2.) In line 18, page 2, for mErB, read mEerR.

(3.) In line 109, page 2, the sign should be inserted after 5,.

(4.) In the 2d, 3d, 4th, 5th, 6th, and 7th claims, in the 4th line of each of said claims, the comma after the Word closed should be omitted;

And it is certified that the proper corrections have been made in the files and records pertaining to the case in the Patent Office, and should be read in said Letters Patent to make the same conform thereto.

Signed, countersigned, and sealed this 19th day of May, A. D. 1885.

[SEAL] H. L. MULDROW,

Acting Secretary of the Interior.

Oountersigned:

M. V. MONTGOMERY,

Commissioner of Patents. 

